Rotatable wave guide joints



Nw mm bau WE. a@ 5M w June 19, 1956 J. G. MCCANN ET A1.

ROTATABLE WAVE GUIDE JoNTs Filed Sept. 5, 1950 2,751,559 .v -.Pa.tented June 1.9, 1.956

ROTATABLE WAVE GUmE JolNfrs Joe G. McCann, Pacific Palisades, and RomarAE. Stein, Los Angeles, Calif., assgnors to Gillillan Bros., Inc., Los Angeles, Calif., a corporation of California Application September 5, 1950, Serial No. 183,264

8 Claims. (Cl. 333-97) The present invention relates to an improved joint construction useful in a wave guide assembly wherein it is desired to prevent leakage of high frequency energy and deterioration of the associated bearing structure as a result of such energy.

Heretofore bearing troubles have been encountered in installations, such as in rotatable wave guide sections used to transmit high frequency energy to a rotating plan position search or surveillance antenna. The energy is usually fed-to the rotating antenna through a Wave guide comprising a central relatively stationary inner metal conductor and a coaxially arranged outer conducting and rotating sleeve. Since the sleeve rotates, it is necessary to provide a hearing structure for supporting and guiding the sleeve or outer Wave guide conductor in its rotational movement.

Itis highly desirable, to conne all of the high frequency energy between the inner and outer Wave guide conductors, i. e., Within the wave guide, and to prevent the escape of the radio'frequency energy through the annular opening dened by the end of the rotating sleevelike conductor and its spaced relatively stationary continuation. This usually involves the use of a half wave closed cavity in communication with such opening, so that such opening is electively short .circuted, electrically speaking.

However, it has been observed that even though elaborate precautions are taken in an attempt .to .achieve such a half Wave cavity and resulting zero impedance at such annular opening, some energy does leak through such opening and appears along -the outside stu-.face of the outer rotating sleevelike conductor to produce deteriorating eiects on the neighboring bearing structure used to support and guide `the same in vits rotational movement. This undesirable result is produced by the -fact `that the bearing structure is in series with a :section of the cavity. The bearing structure consequently isin a region of high voltage and arcing .may `occur 4between relatively movable parts ofthe bearing tocausedetecioration Lof the same.

The present invention contemplates the provision .of an improved technique and means whereby Vthe .bearing is not appreciably subjected to the high frequencyenergy and the aforementioned `undesirable results are no longer present.

-lt ris therefore an object of the present .invent-ion -to `provide improved means and technique whereby .aforementioned new and improved results are achieved.

A speciic object of the present invention -is to provide an improved rotating wave guide joint in which the guide `across fthe bearing structure, thereby vprevei:\tin, .1, .the high frequency vener-gy 'from producing deleterious effects .on the bearing.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. This invention itself, both as to its .organization and manner of operation, together With further objects and advantages thereof, may be best understood voy reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 is a cross sectional view through a portion of rotating antenna structure which incorporates a wave guide for feeding energy thereto, in accordance with features of the present invention; n

Figure 2 is -a perspective view, partly in section, of some of the elements shown in Figure 1;

Figure 3 shows two Wave guide like cavities, the .electrical equivalent of the mechanical arrangement shown in Figures 1 and 2.

Although it is clear that .the present invention is applicable to any wave guide construction `wherein there is relative movement 'between the inner .and outer conductors of the coaxial Wave guide,the invention is shown incorporated in Figure l as a part Aof a plan position, search surveillance antenna wherein the inner `conductor comprises .a stationaryhollow metal tube 10 and an .outer rotating sleeve 11. The sleeve 111s rotatable with respect to the stationary `base 12, whichscrew threadedly receives the protective stationary casing 14, such .casing 14 serving, in conjunction with the'hearings l5., l5', .to guide the movement of the rotating Wave guide sleeve 11. The outer race 15A .of .the bearing 15 may be ,axed to the protective sleeve 14 .so as .to remain stationary, whereas the inner race ESB may be secured directly .to the shouldered tube llA (Figure l) which is atxed to the rotating sleeve V11, and for present intents and purposes may be considered to be' a part ofthe same. These races 15A, lSB may .be .secured to their respective members using many diercnt mechanical .expedients ,such as, for example, by presstting, wedges, or hy use of a cooperating grooved structure, the details .of whichj Per se, form no part of the .present invention.

Since vthe sleeve 1.1 rotates with respect .to .the .base 12, there arises by necessity, van annular clearance opening 16 between such members 11, i2. The vpresent invention concerns itself particularly with .the leakage of vhigh frequency energy through this .annular opening 16 which may result under various circumstances. In order to minimize the undesired escape of .energy .through such .space 1.6, such space 16 is Lin communication with the wave guide type of .cavity which consists of the sections 17A and 17B which have a total length Substantially equal .to one 7half the .Wave length O Ille high frequency energy introduced into the wave guide. The frequency of this energy may be in the Order of, for example, 2800 megacycles, which corresponds .approximately to a wavelength .of 10.7 centimeters.

The cavity 17A is defined b y the .Space between, .on the one hand, the annular ring-shaped flange 12A on .the 'base 12, and, on the other hand, the .adjacent cuter Wall of .the rotating sleeve 11. The cavity `17B .is dened by the space between, on the one hand, the YSame annular ange 12A, and, on the other hand., .the .adjacent wall of the integrally formed ring portion 12B of `the base 12. Each of these sections 17A, 17B .is essentially one quarter wave lengthlong, as indicated 'in -Figure 3.

1n Figure 3 the annular opening 16 is indicated between the Ysmall circles 20, 2-1 and vis in communication with a source of high frequency voltage. The Vbottom Aof the Vslot 17E defined 'by 'the spaced anges 12A and .12B jis indicated by the short conductor 17E. The distance vfrom ithe annular :opening #16 to vthe 'inner annular v `svall 17E Iis .one half a wavelength.

a ln accordance with 1an.important:feature.et `themesent inventlon, k.the .bearing .fis :spaced zfrem the xwave guide type of cavity 17A, 17B a distance equal to one quarter of a wave length and is spaced from the opening 16 a distance equal substantially to one half a wave length through the wave guide type of cavity 17C. This spacing is represented in Figure' 3.

In analyzing the electrical behavior of the structures shown herein, attention is directed to the fact that a wave guide closed at one end and equal to one half a wave length or a multiple thereof, reflects a solid wall where it joins another wave guide. In this instance the parts defining the wave guide sections 17A, 17B, as well as the Wall 17E are of metal, and the metallic wall 17E effectively appears at the opening 16, thereby preventing or minimizing greatly the flow of radio frequency energy through said opening 16. Nevertheless, even though a solid ywall is thus reflected, some energy is transmitted through the sections 17A, 17B, although such energy is not necessarily dissipated, except for the normal losses which occur along the walls of the wave guide.

Heretofore, the bearing was effectively placed in series with the Wave guide sections 17A, 17B at a position of relatively large potential gradient, with the result that arcing would occur between the components of the bearing, especially when a thin film of insulating lubrication separated them. For example, small pits formedY from electrical discharges have been observed in the outer spherical surface of the balls 15C disposed between the bearing races 15A and 15B. These pits have, of course, impaired the operation of the bearing and have led to other undesired and bothersome secondary effects in the operation of the radar system incorporating the antenna structure.

Such undesired and bothersome effects are eliminated in accordance with the present invention by spacing the bearing 15 a quarter of a wave length from the wave guide 17A, 17B, and a half wave length from the opening 16. VAssuming that the resistance of the bearing 15, i. e., the resistance measured between races 15A and 15B, is relatively small, its impedance is reflected kas a solid wall at the opening 16. Also, since the bearing 15 is spaced athalf wave length from the opening 16, it is in a region of low potential gradient where arcing does not occur. Thus effectively two solid walls are reflected at the opening 16, one wall being due to wall 17E and the other wall being due to the low resistance bearing 15.

Assuming that the bearing 15, saturated with insulating lubricant has a relatively high resistance, then the solid wall reflected at the opening 16 due to the half wave spaced wall 17E is still operative and the high resistance of the bearing 15 appears as a low resistance, i. e., a solid wall one quarter wave length away at the junction point of Wave guide 17C, guide sections 17A and 17B to minimize the flow of energy to the bearing 15.

This is in accordance with the theory that a quarter Wavey length line inverts a load impedance whereas a half "wave line repeats the load impedance. Y

While the particular embodiments of the present invention have been shown and described, it will be obvious. Y to those skilled in the art that changes and modifications may be madeiwithout departing from this invention in its broader aspects and, therefore, the aim in the aprespect to said base, `an annular opening defined between Y said sleeve and said base through which high frequency energyV may leak, said base having a wall cooperating with the outer wall of said' sleeve and defining therewith a rst cavity section, said cavityrrsection having one of its ends in `communication Iwith said annulanopening,

a second cavity section extending between said bearing means and the other end of said first cavity section, a third cavity section in said base having one of its ends terminating at a wall in said base and having the other one of its ends in communication with said other end of said first section, each of said first, second and third cavity sections being one quarter wave length long, each of the designated wave lengths being the wave length of said high frequency energy as measured in the corresponding cavity section.

2. The arrangement set forth in claim l in which an Y outer sleeve isV mounted on said base, and said bearing means being disposed between said outer sleeve and said annular sleeve.

3. In a rotatable wave guide construction arranged to guide energy of high frequency, a base, an outer sleeve mounted on said base, an inner annular sleeve rotatably mounted on said base, bearing means disposed between said inner and outer sleeves, a conductor mounted on said base within and extending coaXially with both said inner and outer sleeves, an annular opening defined between said inner sleeve and said base through which high frequency energy may leak, said base having a Wall cooperating with the outer wall of said sleeve and defining therewith a first cavity section, said first cavity section having one of its ends in communication with said annular opening, a second cavity section Vextending between said bearing means and the other end of said first cavity section, a third cavity section in said base having one of its ends terminating at a wall in said base andhaving the other one of its ends in communication with said other end of said first section, each of said first, second, and third cavity sections being one quarter wave length long, each of the designated wave lengths being Vthe wave length of said high frequency energy as measured in the corresponding cavity section. Y

4. In a rotatable wave guide joint construction arranged to guide energy of high frequency, a relatively stationary base, a relatively rotatable sleeve mounted on said base with an annular clearance opening dened by said sleeve and said base through which high frequency energy may leak, bearing means rotatably supporting said sleeve with respect to said base, a rst half wave length wave guide type cavity having one end defined by said opening, said half wave length cavity terminating at its other end in a short circuit whereby the impedance which it presents at said opening is substantially zero impedance, said bearing means being at one end of a further cavity which communicates at its other end with "said half wave length `cavity at an intermediate portion thereof, the length of said further cavity plus the distance from said intermediate portion to said `opening being onehalf a wave length whereby said bearing means is in communication with ysaid opening through a half wave length cavity which includes said further cavity and a portion of said half wave length cavity, earch of the designated wave lengths being the wave length ofsaid high frequency energy as measured in the corresponding cavity.

5. A'construction as defined in claim 4 wherein lsaid intermediate portion is at the center of said half wave length cavity and wherein'the length of said further cavity is a quarter wave length, said bearing means comprising moveable and stationary members with the resistance therebetween being relatively low whereby the impedance reiiected thereby to said opening is low and constitutes, in effect, a solid wall. v Y

6. A construction as defined in claim` 4 wherein vsaid intermediate portion is at the center of said half wave length cavity and wherein the length of said further cavity is a quarter wave length, said bearing means comprising moveable and stationary members with the yresistance therebetween being relatively high whereby the impedance reflected thereby to said opening is high and constitutes, in effect, a solid wall. 4

2,751,559 5 6 7. A construction as dened in claim 4 wherein said wave length cavity being defined by the space between intermediate portion is at the center of said half wave said sleeves. length cavity and wherein the length of said further cavity I is a quarter wave length, said short circuit comprising a References Cited m the me of thls Pmet wall at said other end of said half wave length cavity. 5 UNITED STATES PATENTS 8. A construction as defined in claim 4 wherein said 2,470,805 Collard May 24, 1949 base includes an outer sleeve surrounding a portion of 2,494,691 Cork et aL Jam 17, 1950 said rotatable sleeve adjacent said opening and spaced 2,513,205 Roberts June 27, 1950 therefrom, said bearing means comprising antifricton de- 2,561,130 McClellan July 17, 1951 vices between said sleeves, at least a portion of said half w 2,572,970 Baker Oct. 30, 1951 

